Mark O'Mara, the new attorney for George Zimmerman, tells TODAY's Carl Quintanilla he was surprised his client was charged with second degree murder in the shooting death of Trayvon Martin.

Legal experts expressed surprise that a Florida state prosecutor is seeking a second-degree murder charge against George Zimmerman, the block watch volunteer who fatally shot 17-year-old Trayvon Martin during a scuffle, given that he wasn't arrested or charged the night of the fateful altercation.

Zimmerman’s legal team is expected to invoke the controversial “Stand Your Ground” provision of Florida law as a key strategy in defending him against the charge, which was announced Wednesday evening by Special Prosecutor Angela Corey.

"It seems like an enormous swing to be able to go from not feeling you have enough evidence to arrest him, to charging him with essentially as high as you can charge him in second-degree murder," Richard Hornsby, a criminal defense attorney in Orlando, Fla., told msnbc.com. "Second-degree murder requires him to have engaged in an intentional act with ill will, hatred or spite. It means he basically went and was looking to shoot Trayvon Martin."

Other legal experts have pointed out that no one has had access to all the evidence in the case that the prosecutor has seen. Plus, a jury could decide to convict Zimmerman of the lesser charge of manslaughter.

The lack of an immediate arrest or charges in the case had sparked protests in many cities around the country and inflamed debates about race and crime in America. Martin was black. Zimmerman has a white father and a Hispanic mother.

Florida special prosecutor Angela Corey announced George Zimmerman has been charged with second-degree murder in the shooting death of Trayvon Martin. NBC's Kerry Sanders reports.

Zimmerman could face up to life in prison if convicted of second-degree murder.

Zimmerman's attorney Mark O'Mara said his client would plead not guilty to the charges. He asked people not to jump to conclusions about his client's guilt.

Zimmerman is likely to be tried before a jury in Sanford, Fla., where the killing took place Feb. 26, though defense attorneys may argue that the trial should be moved to another jurisdiction, according to NBC News. Two attorneys who earlier worked with Zimmerman quit the case on Tuesday.

NBC News legal analyst Kendall Coffey, a former federal prosecutor, called the charges "aggressive," and Corey's presentation of seeking justice in the case "masterful" for emphasizing that she was following the law. Shortly before the charge was announced, Coffey said prosecutors likely face a difficult time at trial.

If the defense can successfully argue that George Zimmerman was acting in self-defense, a judge could dismiss the case. NBC's Savannah Guthrie reports.

“Bottom line is there is very big difference between a righteous prosecution and an easy prosecution,” Coffey told msnbc TV. “I think she believes in her heart and in her mind that this is a righteous prosecution and the chips are going to fall where they may.”

Critical to the defense is the 2005 Florida "Stand Your Ground" law, which says a citizen doesn’t have to retreat before using deadly force against an attacker, legal experts say. The law also can let a judge, in an evidentiary hearing before a jury trial, determine that a defendant can’t be prosecuted due to the self-defense argument.

Corey will need to prove that Martin’s death was caused by a criminal act of Zimmerman, and that the act was “demonstrating a depraved mind without regard for human life,” NBC News reported.

“There’s no telling what happens here. Say what you will about the case, it’s not a slam-dunk in terms of the evidence,” Savannah Guthrie, chief legal analyst at NBC News, said shortly before charges were brought. “There’s conflicting evidence and in our system the tie goes to the accused. Innocent before proven guilty.”

According to legal experts, the first hurdle for prosecutors will be that special evidentiary hearing that is part of the “Stand Your Ground Law.” In it, Zimmerman can argue that he deserves immunity from the charges because he was acting in self-defense.

But to convince the judge, Zimmerman will have to present a "preponderance of evidence" that he acted in self-defense, which means he will have to show he had a "reasonable belief" that such force was necessary. Though the “preponderance” standard is less than “reasonable doubt” of a full trial, it is difficult to prove, criminal defense attorneys say, and many judges have frowned on deciding such cases on their own.

After the press conference announcing George Zimmerman was in custody and would face a second-degree murder charge, Trayvon Martin's parents spoke to reporters, saying they were thankful that there was an arrest, and that 'this is just the beginning.' NBC's Ron Allen reports.